I work on media files as per my profession. I find my Mac (Mac Lion) going slower day by day. I think it will be beneficial to defrag the drive but didn't find any Apple tool for it. I want a an effective third party Mac defragmenter for my Mac drive.

@WojciechBednarski Every hard drive suffers from fragmentation. SSDs have a extremely fast access time compared to mechanical drives, therefore it is less visible. SSDs have a limited number of read/write cycles for each one of it's cells, you win some, you loose some...
– FredNov 9 '11 at 13:31

On APFS - you don’t need to defragment anything.
On HFS+ - DriveGenius does what you ask. It rebuilds the catalog (filesystem) that tracks the files. You don’t need to rearrange the files on the drive as macOS does that for you - just keep 20 GB free or 25% free if you can, and the system optimizes the file location automatically.

There aren't many apps that do this on mac since actual filesystem fragmentation both rare and rarely a cause of measurable slowdown.

Mac OS X automatically defragments files that are likely to cause a slowdown in addition to automatically optimizing hot (often used) files to a fast and not-fragmented part of the drive.

The HFS+ filesystem directory / catalog itself can become fragmented over a long time but you can fix that easily. Back up to time machine and an erase install / migration back cures that issue without needing to spend money on a live tool. DiskWarrior also helps to rebuild HFS+ catalogs in addition to the already mentioned Drive Genius.

Best of luck - keep looking if you find defrag isn't what the doctor ordered on your mac.

I agree with Mark. Usually, I don't fill up a drive past 80-85%, as the slower parts of a mechanical drive begins around that point. HDs have different speeds and access time depending on the location on the disk.

Therefore using an app like iDefrag could help (remember to backup your files before!) but will likely need to be done on a regular basis to provide a continued result, and I'm wondering if the time you're gonna spend on this isn't gonna be for nothing.

I would suggest using RAID-0 or better yet RAID-5 drives setups. Bit more expansive, but speed will be much more constant over a longer period of time, but this setup also carries more risk (especially RAID-0), therefore you NEED a backup, could get expensive...

An SSD is a good solution, the only problem is the capacities. A good, fast and reliable 204 Gb SSD retails for ~500$, a 480 Gb for ~900$.